Irregularities in the terrain over which a tracked vehicle travels produce displacements and deflections of its suspension system. Depending upon their magnitude, frequency and strength, these deflections cause more or less discomfort to the operator and passenger of the snowmobile.
The dynamic response of a rear suspension assembly of a tracked vehicle such as a snowmobile, to the multitude of loads imposed upon it during operation, has a significant effect on the overall performance of the vehicle and rider comfort. Different types of loads are regularly exerted upon a tracked vehicle. A first type of loads results from impact loads imposed upon the rear suspension as the vehicle travels over rough terrain and encounters bumps, these are of the most concern. A second type of loads results from loads resulting from acceleration and deceleration. The internal forces that are developed during rapid acceleration cause a weight transfer from the front of the vehicle to the rear. This tends to lift the skis off the ground and thus interferes with steering. The internal forces developed during rapid deceleration cause, however, a weight transfer from the rear of the vehicle to the front. This tends to compress the front of the tunnel toward the front of the slide rails. The complex interaction of the forces which occur in the rear suspension assembly during operation have demanded optimal design of mechanisms for absorbing and attenuating the complex combination of loads imposed upon a modern high performance snowmobile.
Conventionally, the rear suspension supports the endless track, which is tensioned to surround a pair of parallel slide rails, a plurality of idler wheels and at least one drive wheel or sprocket. A shock absorbing mechanism involving compressed springs, hydraulic dampers, and/or other shock absorbing elements, urges the slide frame assembly and the chassis (also known as a frame) of the snowmobile apart, against the weight supported above the suspension in a static condition.
One example of a conventional rear suspension of a snowmobile is described in U.S. Pat. No. 5,727,643, issued to Kawano et al. on Mar. 17, 1998. Kawano et al. discloses a suspension device for providing a resilient support for a snowmobile body, including a frame for supporting the snowmobile body. A slide rail is operatively connected to the frame for pressing a crawler belt against a snow surface. A swing arm includes a first end pivotally supported on the frame and a second end pivotally mounted on the slide rail. A shock absorber assembly includes a first end pivotally supported on a shaft adjacent to the first end of the swing arm, a second end of the shock absorber assembly being connected to the frame through a progressive link pivotally supported on the swing arm.
Another example of a conventional rear suspension of a snowmobile is disclosed in U.S. Pat. No. 5,904,216, issued to Furusawa on May 18, 1999. Furusawa discloses a rear suspension of a snowmobile including two angular suspension arm assemblies, which connect the slide frame assembly to the snowmobile chassis. These suspension arm assemblies are moveable independently of one another in order to permit the slide frame assembly to react to static and dynamic forces arising during operation. A single cushion unit extends horizontally and is operatively connected at opposed ends thereof to the respective suspension arm assemblies in order to support and attenuate the loads.
Although conventional rear suspension systems available provide a relatively comfortable ride to the passengers, it is desirable to further improve the rear suspension assemblies for tracked vehicles, particularly snowmobiles. It is also desirable to provide a rear suspension assembly that would be designed to reduce effects due to acceleration and deceleration loads.